1. Field of the Invention
This invention relates to a surface optical device apparatus which can be readily fabricated with good yield and is suitable for use in a structure constructed in a one- or two-dimensional array, its fabrication method, an optoelectronic device in which the surface optical device is integrated together with a Si integrated circuit (Si-IC), an optical wiring device using the surface optical device apparatus, an optical recording apparatus using the surface optical device apparatus, and related structures and devices.
2. Related Background Art
In recent years, the development of surface light emitting devices arranged in two-dimensional arrays has been desired. Among such devices, a vertical cavity surface emitting laser (VCSEL) is strongly expected since its threshold is low (approximately 1 mA), its power consumption is small, and it can be easily arrayed. Moreover, when a VCSEL is integrated with a Si-IC, the VCSEL can be speedily driven, and the device can be presented in a small package. Accordingly, such a structure can be advantageously applied to signal transmission between Si-IC""s, to optical recording on a recording medium, and similar uses.
There are several methods of integrating an optical device and a Si-IC. In one method, an optical device is bonded to a Si substrate wherein Si-IC has been formed. In another method, a Si-IC and an optical device are integrated in a hybrid manner on a supporting substrate, such as a Si substrate, a printed circuit board (PCB), or a ceramic substrate.
As an example of the former method, there exists, as disclosed in Japanese Patent Application Laid-Open No. 9(1997)-223848, a method in which an epitaxial growth surface of a laser radiating layer is bonded to a Si-IC via a polyimide adhesive, and a GaAs growth substrate, on which the laser radiating layer had been grown, is removed by etching to obtain a surface emitting laser. FIG. 1 illustrates a cross section of this structure. An electrode of the surface emitting laser 100B fabricated by the above process is connected to an electrode 200A on the Si-IC substrate 200 via electrical wiring 400. Another electrode 100D is connected to a wiring pattern formed on the insulating layer 300 of polyimide. In such a structure, no alignment is needed between the optical device and the Si-IC. Further, additional processing, such as photolithography, can be conducted even after the integration, since only a functional layer of the optical device without its growth substrate is arranged on the Si and a step of the surface is hence small (about 5 xcexcm). In FIG. 1, a light receiving device 100A, an electrode 100C of the device 100A and a layer 1000 of optical devices are illustrated as well.
As an example of the latter method, there exists, as disclosed in Japanese Patent Application Laid-Open No. 7(1995)-30209, a method in which a semiconductor substrate of an optical device is removed, the optical device in chip form is bonded to a film or the like, and the optical device is aligned with an electrode of an electronic circuit substrate and implemented in a flip-chip manner. FIGS. 2A to 2H illustrate the fabrication steps according to this method. After a functional layer 1106 is epitaxially grown on the semiconductor substrate 1101 as illustrated in FIG. 2A, an electrode 1109 for driving the optical device 1111 is formed as illustrated in FIG. 2B. The devices 1111 are then separated as illustrated in FIG. 2C, and the semiconductor substrate 1101 is removed by etching as illustrated in FIG. 2D. The devices 1111 are bonded to an extensible film 1114 as illustrated in FIG. 2E, and the film 1114 is extended to obtain chips of the optical device 1111 with only the functional layer 1106 as illustrated in FIG. 2F. The optical device 1111 is affixed at a desired area of an electronic circuit board 1117 with a pressing jig 1116. Thus, an optoelectronic multi-chip-module (MCM), in which the optical device 1111 is placed on the electronic circuit substrate 1117 in a hybrid integration manner, as illustrated in FIG. 2H, can be obtained. In FIGS. 2A to 2H, there are also illustrated a buffer layer 1102, a lower mirror 1103, an active layer 1104, an upper mirror 1105, an anode 1107, a cathode 1108. a mesa groove 1110, a separating groove 1112, a protective layer 1113, a spacing 1115, and an electrical wiring 1118.
There are significant problems with the structure disclosed in Japanese Patent Application Laid-Open No. 9(1997)-223848, however. Its thermal radiation characteristic is poor, and its luminary characteristics, such as light radiation efficiency and light output, are inferior to those of ordinary implementation structures, since the polyimide layer 300 is interposed between the optical devices 100A and 100B and the Si substrate 200. Further, since the fabrication process of the optical devices 100A and 100B is performed only after the functional layers of the optical devices are transferred to the Si substrate 200, limitations on the freedom of the process (i.e., on processing temperature, plasma processing, and the like) arise, due to concerns with preventing damage to the IC. Accordingly, the configurations of the optical devices 100A and 100B are also restricted.
Concerning the structure of Japanese Patent Application Laid-Open No. 7(1995)-30209, its mechanical strength is low due to a small thickness (ordinarily about 5 xcexcm) of the functional layer 1106 without the substrate, though its thermal conductivity is good due to direct bonding between the electrodes. Accordingly, its handling is difficult, and its performance characteristics are likely to be decreased due to the introduction of crystallographic defects therein, and the like. Furthermore, two electrodes must be aligned for each device since the electric contact should be established on the side of the circuit board 1117 only. Therefore, high alignment precision is required, and costs increase accordingly.
It is an object of the present invention to provide an apparatus with a surface optical device, in which characteristics of the surface optical device are not decreased with the integration of the surface optical device and the electronic device, where no high precision of alignment is required at the time of implementation, and whose productivity is high. It is a further object of the present invention to provide a method of fabricating such an apparatus, as well as other apparatuses which use such an apparatus, such as an optoelectronic MCM, an optical wiring apparatus and an optical recording apparatus, and related structures and methods.
The present invention is generally directed to a surface optical device apparatus including a surface optical device, and a second substrate. The surface optical device includes a functional layer grown on a first substrate, which acts as a supporting substrate needed for fabricating the functional layer thereon, with the first substrate being later thinned or removed, and a first electrode formed on at least one of the surfaces of the functional layer. The surface optical device emits or receives light in a direction approximately perpendicular to the first substrate, and the first electrode has a function for electrically controlling the light emission or reception. The second substrate includes a second electrode formed thereon, and the surface optical device is bonded to the second substrate with the first electrode and the second electrode being in electrical contact with each other. In the apparatus of this invention, the first substrate is removed or thinned by etching or the like after the optical device is bonded to the second substrate, such as a Si substrate or a circuit substrate, with the first and second electrodes electrically connected, and another electrode is led from a surface of the optical device exposed after the first substrate is removed or thinned. Accordingly, the thermal characteristic of the surface optical device is improved due to the close proximity of the second substrate to an active layer of the optical device, and thus, no high alignment precision is required at the time of bonding the optical device. Further, the first substrate still remains after the optical device has been bonded, so that the optical device can be readily handled without damaging the functional layer.
The following more specific structures are possible in the above structure.
The second substrate may further include first electrical wiring, electrically connected to the second electrode.
A plurality of surface optical devices may be arranged on the second substrate, and the second substrate may further include second electrical wiring for independently driving and controlling the surface optical devices. In this case, the first electrode may be formed on the surface of the functional layer on a side opposite to the side of the first substrate, as a common electrode, the plurality of the surface optical devices may be separated from each other, a third electrode may be formed on each surface optical device on the side of the first substrate, and the second electrical wiring may be connected to the third electrode. Further, in this case, the second electrical wiring may be formed on an insulating layer formed on the surface optical device on the side of a third electrode, and a contact hole for electrically connecting the third electrode to the second electrical wiring, and a window for transmitting light, may be formed in the insulating layer. Thus, the optical devices can be independently driven and controlled, and an array of surface optical devices can be obtained with high productivity without diminishing the characteristics of the optical devices.
A plurality of the surface optical devices may be arranged on the second substrate, the surface optical devices may be separated from each other, a third electrode may be formed on each surface optical device on a side opposite to the first electrode, the second substrate may further include first electrical wiring electrically connected to the second electrode, and second electrical wiring electrically connected to the third electrode, and the first electrical wiring and the second electrical wiring may construct a wiring matrix for independently driving and controlling the surface optical devices. Thus, a two-dimensional array of surface optical devices can be obtained with high productivity without diminishing the characteristics of the optical devices. In this case also, the second electrical wiring way be formed on an insulating layer formed on the surface optical device on the side of the third electrode, and a contact hole for electrically connecting the third electrode to the second electrical wiring, as well as a window for transmitting light, may be formed in the insulating layer.
The surface optical device is typically a surface emitting laser with the functional layer including an active layer and distributed Bragg reflector (DBR) mirror layers sandwiching the active layer.
The present invention is also directed to an optoelectronic multi-chip module (MCM) including a surface optical device, a second substrate, and an integrated circuit for driving and controlling the surface optical device. The surface optical device and the second substrate are constructed as described above in connection with the surface optical device of this invention. The integrated circuit, such as a bare chip of a Si-IC, is provided on the second substrate, and electrically connected to the surface optical device through the second electrode. Thereby, the IC and optical device can be integrated in a compact structure, and an electrical signal can be converted into an optical signal.
The integrated circuit, as described, may be a bare chip of a Si integrated circuit which is implemented on the second substrate in a flip-chip manner. Thereby, an optoelectronic MCM with high productivity can be obtained.
The second substrate may be a Si substrate, and the integrated circuit may be a Si integrated circuit which is fabricated in the Si substrate.
The present invention is also directed to an optical wiring device in which an optical waveguide medium, such as an optical fiber, is fixed to the surface of the surface optical device of an optoelectronic MCM of this invention to perform optical transmission and reception through the medium of the optical waveguide. The optical waveguide medium is perpendicularly fixed to the surface of the surface optical device with a resin adhesive. Thereby, a high-speed optical wiring device with low electromagnetic radiation emission noise (EMI) can be obtained at a low cost by using the MCM of this invention.
The present invention is further directed to a multi-layer optoelectronic multi-chip module (MCM) including a plurality of optoelectronic multi-chip modules and an inter-layer insulating layer which is flattened and provided between the respective optoelectronic multi-chip modules, such that transmission and reception of optical signals can be performed between such optoelectronic multi-chip modules. Thereby, a high-performance optoelectronic MCM capable of performing fast processing can be obtained by stacking a plurality of MCM""s with integrated surface optical device and electronic device.
The present invention is also directed to a multi-layer optoelectronic multi-chip module including a plurality of the optoelectronic multi-chip modules of this invention in which the second substrate is an insulating thin film, and an inter-layer insulating layer which is provided between the respective optoelectronic multi-chip modules, such that transmission and reception of an optical signal can be performed between the optoelectronic multi-chip modules. Thereby, a high-performance multi-layer optoelectronic MCM, capable of performing fast processing, can be obtained.
The present invention is also directed to an optical recording apparatus which includes a light source from the optoelectronic MCM of this invention, and a control unit for controlling the light source to perform recording on an optical recording medium with a plurality of laser beams from the light source. Thereby, a high-performance laser beam printer, a CD-ROM apparatus, an optomagnetic disc apparatus, and the like, can be thus obtained.
The present invention is also directed to a method of fabricating a surface optical device apparatus, which including the steps of:
(a) forming a surface optical device functional layer on a first substrate;
(b) processing the shape, and a first electrode, of the surface optical device;
(c) forming a second electrode on a second substrate;
(d) bonding the surface optical device to the second substrate with the first electrode being aligned with the second electrode; and
(e) removing or thinning the first substrate such that substantially only the functional layer is transferred to the second substrate.
When a plurality of such surface optical devices are arranged, the method may further include the steps of:
(f) removing the functional layer between a plurality of the surface optical devices to separate the respective surface optical devices from each other;
(g) forming a third electrode on each surface optical device;
(h) forming an insulating layer on the transferred functional layer;
(i) forming a first hole for establishing an electrode contact, and a second hole for transmitting light, in the insulating layer; and
(j) forming electrical wiring, electrically connected to the third electrode through the first hole, on the insulating layer and on the second substrate.
According to such a method, a process for integrating the surface optical device and an electronic device can be achieved with high productivity and high yield.
The present invention is also directed to a method of fabricating a surface optical device apparatus, which includes the steps of:
(a) forming a surface optical device functional layer on a first substrate;
(b) processing the shape of the surface optical device;
(c) removing the functional layer between a plurality of the surface optical devices to separate the respective surface optical devices from each other;
(d) forming a first electrode of the surface optical device;
(e) forming a second electrode on a second substrate;
(f) bonding the surface optical devices to the second substrate with the first electrode being aligned with the second electrode;
(g) removing or thinning the first substrate such that substantially only the functional layer is transferred to the second substrate;
(h) forming a third electrode on the transferred functional layer;
(i) forming an insulating layer on the transferred functional layer;
(j) forming a first hole for establishing an electrode contact, and a second hole for transmitting light, in the insulating layer; and
(k) forming electrical wiring, electrically connected to the third electrode through the first hole, on the insulating layer and on the second substrate.
Further, according to such a method, a process for integrating the surface optical device and an electronic device can be achieved with high productivity and high yield.
The present invention is also directed to a method of fabricating a surface optical device apparatus, including the steps of:
(a) forming a functional layer of the surface optical device on a first substrate;
(b) processing the shape of the surface optical device;
(c) removing the functional layer between a plurality of the surface optical devices to separate the respective surface optical devices from each other;
(d) forming a first electrode of the surface optical device;
(e) bonding a surface of the functional layer to a third substrate;
(f) removing or thinning the first substrate such that substantially only the functional layer is left;
(g) forming a third electrode on an exposed surface of the functional layer;
(h) forming a second electrode on a second substrate;
(i) bonding the surface optical devices to the second substrate with the third electrode being aligned with the second electrode;
(j) removing the third substrate such that only the functional layer is substantially transferred to the second substrate;
(k) forming an insulating layer on the transferred functional layer;
(l) forming a first hole for establishing an electrode contact, and a second hole for transmitting light in the insulating layer; and
(m) forming electrical wiring, electrically connected to the third electrode through the first hole, on the insulating layer and the second substrate.
According to such a method, a process for integrating the surface optical device with the electronic device can be achieved with high productivity and yield.
Each of the above methods may further include a step of forming an etching stop layer for selective etching between the first substrate and the functional layer, and the first substrate may be removed by etching which is then stopped at the etching stop layer. In this case, the method may further include a step of removing the etching stop layer after the first substrate is removed.
The present invention is also directed to a method of fabricating a plurality of optoelectronic multi-chip-modules in a collective manner, which includes the steps of:
(a) forming a functional layer of the surface optical device on a first substrate;
(b) forming a plurality of electrodes on a plurality of areas, respectively, on a second substrate;
(c) bonding at least a surface optical device, such as an array of surface optical devices, which is cut out from the first substrate with the functional layer of the surface optical device, to each such area on the second substrate;
(d) collectively removing or thinning the first substrate on the second substrate such that substantially only the functional layer remains on each area of the second substrate;
(e) forming electrical wiring on each such area of the second substrate;
(f) implementing an integrated circuit, such a Si-IC, on each area of the second substrate; and
(g) dicing the second substrate such that the respective areas of the second substrate are separated from each other.
According to this method, a plurality of the optoelectronic MCM""s can be collectively fabricated by a single process, and productivity can be improved.
These advantages, as well as others will be more readily understood in connection with the following detailed description of the preferred embodiments of the invention in connection with the drawings.